This invention relates to droplet deposition methods and apparatus in which droplets are ejected from a chamber on demand via a nozzle by varying the volume of the chamber.
The variation of chamber volume preferably is effected by piezoelectric actuators, for example by deflection of piezoelectric material which bounds the chamber. Such an arrangement is shown in our earlier specification EP 0277703A, incorporated herein by reference. Such devices are characterised by elongated ink-containing chambers with nozzles in the end walls of the chambers (known as an xe2x80x9cend-shooterxe2x80x9d configuration).
A problem with such devices is that during periods of non-use, the ink in the chambers may deteriorate, leading to the accumulation of solid particles at the end of the chamber which may block the nozzle. The same problem may occur, although perhaps to a lesser extent, if the nozzle is in one of the long walls of the chamber eg. mid-way along it (ie. a xe2x80x9cside-shooterxe2x80x9d configuration). The present invention in its preferred embodiments is directed to solving this problem by providing a cleaning flow across the nozzle.
In one aspect, the invention provides a method of droplet deposition comprising varying the pressure of liquid in an elongated chamber by varying the volume of the chamber to eject droplets through a nozzle at one end thereof for deposition, and causing a flow of the liquid in the chamber in excess of that required to replenish the ejected droplets, the flow passing across the nozzle.
In another aspect, the invention provides droplet deposition apparatus comprising an elongated chamber having at one end thereof a nozzle through which in operation droplets of liquid are ejected from the chamber for deposition, means for varying the pressure of liquid in the chamber by varying the volume of the chamber to effect ejection of said droplets and means for causing a flow of liquid in the chamber in excess of that necessary to replenish the ejected droplets, the flow passing across the nozzle.
In a further aspect the invention provides droplet deposition apparatus comprising an elongated chamber having a nozzle through which in operation droplets of liquid are ejected from the chamber for deposition, means for varying the pressure of liquid in the chamber by varying the volume of the chamber to effect ejection of said droplets, means for causing a flow of liquid through the chamber in excess of that necessary to replenish the ejected droplets, the flow passing across the nozzle, and the chamber having a longitudinal barrier around which the flow passes at an end of the chamber.
The nozzle may be in an end wall of the chamber or in a longitudinal wall thereof.
The chamber may be divided longitudinally by a barrier, the liquid flow being in one direction on one side of the barrier and in an opposite direction on the other.
In a side shooter embodiment there may be at one end of the elongated chamber a plenum chamber through which the liquid flows from one side of the barrier to the other, the plenum chamber being such that pressure waves in the liquid in the elongated chamber are reflected by the liquid in the plenum chamber.
At least one wall of the chamber may be formed of piezoelectric material, and may comprise electrodes to deform the material in shear mode by the application of a potential difference thereto.
In a further aspect the invention provides droplet deposition apparatus comprising an elongated chamber having at an end thereof a nozzle through which in operation droplets of liquid are ejected from the chamber for deposition, at least one longitudinal wall of the chamber being formed of piezoelectric material, electrode means for applying a potential difference to the piezoelectric material to deform it in shear mode and thereby effect ejection of said droplets, and a barrier extending longitudinally of the chamber to define a plurality of flow passages therein, an end of the barrier being spaced from the nozzle whereby a flow of liquid from one flow passage to another passes across the nozzle.
The barrier may extend generally plane-parallel to the longitudinal wall.
Alternatively, the longitudinal wall may be divided longitudinally by the barrier.
The piezoelectric material may comprise oppositely-poled regions, one on each side of the barrier whereby application of the potential difference to the material deforms it into a chevron shape.
Alternatively the piezoelectric material on each side of the barrier may comprise oppositely-poled regions whereby application of the potential difference to the material deforms it into a chevron shape on each side of the barrier.
The barrier may contain the axis of the nozzle.
The barrier may comprise a longitudinal wall of piezoelectric material having a first electrode at ground potential on one side of the wall and exposed to the liquid, and a second electrode on the other side of the wall and which is not exposed to the liquid.
Thus the barrier may comprise two said walls, each with a said one side exposed to the liquid, the said other sides of each wall being spaced from and facing towards each other.
There may be comprising an apertured plate disposed between an end of the barrier and structure forming an end wall of the chamber wherein the nozzle is defined.
The invention also comprises a printer operating by a method or including apparatus as set forth above.